1. Field of the Invention
The present general inventive concept relates to a developing unit in which a developer is supplied to a photosensitive medium to develop an image and an electrophotographic image forming apparatus having the same, and more particularly, to a developing unit having an improved configuration in which a residual developer is reduced in a consumed developing unit and an electrophotographic image forming apparatus having the same.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus, such as a laser printer, a facsimile, and a digital copier, scans light on a photosensitive medium charged with a predetermined electric potential, forms an electrostatic latent image, develops the electrostatic latent image with a developer having a predetermined color into a visual image, transfers the image on a sheet of paper, and fixes the image on the sheet of paper to print an image.
FIG. 1 is a cross-sectional view of a conventional electrophotographic image forming apparatus. Referring to FIG. 1, an electrophotographic image forming apparatus includes a case 10 equipped with a charge roller 11, a photosensitive medium 13, a light scan unit 15, a developing unit 20, a transfer roller 17, and a fixing roller 19.
An outer surface of the photosensitive medium 13 is charged with a predetermined electric potential via the transfer roller 11, and an electrostatic latent image corresponding to an image to be printed is formed with a light beam L scanned from the light scan unit 15.
The developing unit 20 has a container 25 in which toner, a developer T, is contained. The developer T is supplied to the photosensitive medium 13 on which the electrostatic latent image is formed to develop an image on the outer surface of the photosensitive medium 13 through an agitator 27, a supply roller 24, and a developing roller 21. The developing unit 20 is formed of a single cartridge with the photosensitive medium 13 and the container 25 containing the developer T, and when all the developer T contained in the container 25 is consumed, the developing unit 20 is changed with a new developer T.
In the developing roller 21, a direct current voltage is applied via a source supply portion (not shown) in order to transfer the developer T supplied in the developing unit 20 using an electrophotographic method to the electrostatic latent image formed on the photosensitive medium 13. A regulation blade 23 regulating a developer amount is provided on the outer surface of the developing roller 21. The developer T transmitted from the developing unit 20 via the developing roller 21 passes between the regulation blade 23 and the developing roller 21 to form a developer layer having a predetermined thickness. Also, a waste developer container 29 containing a waste developer W gathered by a cleaning blade 12 after development is provided in the developing unit 20.
Also, the developing unit 20 includes a sealing film 26 to keep the developer T contained in the container 25 in a sealed state. The sealing film 26 separates the developer T from the agitator 27, the supply roller 24, and the developing roller 21 to keep the developer T sealed in the container 25. Accordingly, the developer T in the container 25 is kept in an initial state until an initial use. That is, the sealing film keeps the developer T stable from changes due to external temperature and humidity, and protects the developer T from leaking. When the developing unit 20 is used for a first time, the sealing film 26 is removed by a user and the developing unit 20 is installed in the case 10.
The electrophotographic image forming apparatus prints an image on paper P supplied via a first or a second paper feeding cassette 31 and 35 and includes a feeding path 41 and a discharge path 45 of the paper P. Pickup rollers 32 and 36 picking up a sheet of the paper P, a feed roller 33 guiding the supply of the picked up paper P, and registration roller 42 for assuring development of an image on a desirable position of the fed paper P are provided on the feeding path 41. The fixing roller 19 and a plurality of discharge rollers 47 are provided on the discharge path 45.
As described above, the image developed on the outer surface of the photosensitive medium 13 is transferred onto the paper P supplied from the first or second feeding cassette 31 and 35 and fed between the photosensitive medium 13 and the transfer roller 17 via the feeding path 41, and is fixed by the fixing roller 19. The paper P on which the image is printed is discharged onto a loading portion 50 provided on the upper portion of the case 10 via the discharge path 45.
The developing unit 20 includes a residual developer detecting sensor 22 for detecting residual of the developer T contained in the container 25. The residual developer detecting sensor 22 is electrically connected to a controller (not shown) in the electrophotographic image forming apparatus. When a residual of the developer T is sensed under a standard value by the residual developer detecting sensor 22, the controller informs the user of the requirement of changing the developing unit 20.
The container 25 in the developing unit 20 may be of different sizes. When the container 25 is replaced with a container of a different size, a new metal mold for the container has to be provided, thereby increasing a manufacture cost. Also, containers 25 of the same size may contain different amounts of the developer T.
All of the developer T provided in the container 25 is not used to print images. Some of the developer T provided in the container 25 remains inside the container 25 until the developing unit 20 is changed, and a residual developer amount in the same type of containers 25 is generally the same. Accordingly, when a small amount of the developer T is provided, waste of the developer T is greater than in a case where a large amount of the developer T is provided. Also, when the developer T is charged without considering a characteristic of the residual developer amount, a difference between an expected number of printed sheets and an actual number of printed sheets increases. Also, when the residual developer is not properly gathered, environmental pollution is caused.